This series has addressed a constituency of scientists possessing
biochemical background with the goal of providing them with specialized
reviews of neu- robiological interest. Since its initiation,
neurochemistry and neuroscience have come of age, and the editors
initiate with this volume the concept of a central theme. It is planned
that each subsequent volume will also be topical. We note with sadness
the passing of Dr. Henry Mahler who served as an advisory editor since
the initiation of this series. He played a major role in building the
bridge between biochemistry and neurochemistry and will be missed. Weare
pleased to welcome two new editors, Drs. William Norton and Bruce
McEwen. B. W. Agranoff M. H. Aprison vii FOREWORD Oligodendroglia
constitute one of the three principal cell types of the central nervous
system. These cells, together with their elaborated membranes, account
for at least 25 percent of the dry mass of an adult rat brain and an
even greater percentage of the central nervous system of larger animals.